Ocean Acidification Causes Squid Brains to Shrink

Linked to rising CO2 concentrations in the atmosphere, ocean acidification weighs heavily on marine life, as demonstrated by new experiments conducted on squids.

A Real Threat

The cephalopods are renowned for their remarkable cognitive abilities. Belonging, like cuttlefish and octopuses, to the sub-group of coleoids, they possess a brain neuron count comparable to that of a dog, making them the most “intelligent” invertebrates in the world.

Like many other marine species and ecosystems, whether mollusks, crustaceans, or coral reefs, these fascinating creatures are affected by the acidification of the oceans.

To clarify the impact of this phenomenon on their physiology and behavior, Garette Allen from Acadia University in Canada and her colleagues conducted experiments involving two tanks.

The water in the first tank showed a pH of 8.2, corresponding to the current average of the oceans, while the second tank did not exceed 7.8, the oceanic pH level projected by climate models for 2100.

Physiological and Behavioral Changes

After 90 days, the brain structure and size of the large-fin squids (Sepioteuthis lessoniana) studied were analyzed using an MRI device. On average, the individuals kept in the second tank showed a brain volume 49% smaller, possibly linked to oxidative damage.

The greatest reductions in volume concerned the cephalopods’ visual system. More specifically, the optic lobes (52%) and the optic pathways (62%), responsible for processing information transmitted from the retina.

“In individuals exposed to higher acidity from hatching, we also observed a 42% reduction in hunting behaviors,” the researchers explained at the annual meeting of the Society for Experimental Biology.

Earlier, a study had revealed that ocean acidification was reaching alarming depths.